A conventional, commercially available internal combustion engine utilizes a crankshaft to transform a reciprocating piston motion into a rotary motion. As the piston moves within its cylinder in response to expanding gases of combustion, rotary motion is imparted to the crankshaft through a connecting rod. One end of the connecting rod is affixed to a wrist pin pivotally secured to the piston, while another end is rotatably journaled about an offset throw of the crankshaft. When multiple cylinder arrangements are desired, the crankshaft is extended to include an additional offset throw for each piston connecting rod.
As the piston transmits force created by the combustion of fuel to the crankshaft by way of the connecting rod, the angularity of the connecting rod causes a considerable side thrust to be exerted by the piston on the walls of the cylinder. Such thrust is generally absorbed by a skirt portion of the piston; that is, the section below the piston rings. Further, this side thrust or angular force absorbs a portion of the linear energy and contributes to the inefficiency of the conversion of the linear movement of the piston into the rotary movement of the crankshaft.
In a conventional internal combustion engine, the crankshaft is supported by main bearings, and at the end of the crank throw, a crank pin holds the connecting rod. In order to compensate for energy lost to angular forces, the piston rod is lengthened and the crank throw is made longer than the radius of the cylinder bore. Thus, additional space must be allowed to accommodate the crank throw. In addition, to avoid a downward thrust of the piston while the piston is at the upper limit of the stroke (top dead center), the crankshaft or crank pin may be offset from the longitudinal center of the cylinder, or alternatively a timing mechanism may be employed to delay spark ignition in the combustion chamber. These factors further contribute to increased size of commercially available internal combustion engines.